In a conventional printing apparatus according to an inkjet scheme using thermal energy, the electrothermal transducer (heater) and a drive circuit therefor in a mounted printhead are formed on a single substrate using a semiconductor process, as disclosed in, e.g., EP A2 532877. A technique of forming, on the same substrate, an element for detecting substrate states such as a substrate temperature, resistance value distribution state, and a variation in characteristic of the drive circuit has also been proposed.
As an example in which a circuit block for detecting a substrate temperature is formed on a single substrate, EP 0980758 A proposes a printhead with a circuit formed on an element substrate, which outputs temperature information as a digital signal. In the circuit arrangement formed on the element substrate, digital circuits such as an inverter or a shift-register and analog circuits such as a comparator are mixed.
Components used for these analog circuits are generally designed for use at a power supply voltage of 5 V to sufficiently exhibit its characteristic. However, an inverter or shift register is a digital circuit and basically operates in accordance with a Hi/Lo pulse. An application pulse for a print information interface of the printhead or heater drive is also a digital signal. Signal transmission/reception to/from an external device is done in accordance with a Hi/Lo logic pulse.
Conventionally, the amplitude of a logic pulse used in these circuits and external signal generation circuits is generally 0 V/5 V. As a result, a single power supply voltage of 5V can be used for both the analog circuits and the digital circuits.
Recently, micropatterning for an MPU (microprocessor) or gate array manufactured by a semiconductor process is becoming more popular, and the power supply voltage to be used also tends to be lower. Even for a digital circuit used in an external signal generation unit of a printhead, a power supply voltage of 3.3 V is becoming popular in recent years.
Consequently, a demand has arisen for a semiconductor substrate for a printhead, which has power supply voltage as low as 3.3 V. A digital circuit portion can be driven at a low voltage by, e.g., micropatterning a transistor in the circuit. However, for an analog circuit portion, it is difficult to reduce the drive voltage without changing the circuit arrangement. To reduce the drive voltage of an analog circuit, the circuit must be re-designed. In addition, use of a specific component is also necessary to prevent the characteristic from degrading.
For this reason, in a case where the power supply voltage for the digital circuit is made to 3,3V, a digital circuit uses a power supply voltage of 3.3 V, and an analog circuit uses a power supply voltage of 5 V. Since different power supply voltages are required, the semiconductor substrate of a printhead should be designed to receive two types of power supply voltages from external circuits. This increases the cost and complexes the system configuration, resulting in disadvantages from the viewpoint of space saving or energy saving (power consumption).